A 27-year-old man has been arrested by Major Investigation Team detectives investigating the murder of Malcolm McKeown.
The 54-year-old victim was found dead in his car behind a service station in Waringstown in August.
He had been shot six times to the head and body.
Two men have already been charged in connection with the murder.
The latest to be arrested was detained in the Belfast area today (Wednesday).
He remains in custody this evening.